Pavarotti had been taken to hospital last month, but was released on August 25 after having more than two weeks of tests and treatment.
After surgery in July last year in New York, Pavarotti retreated to his villa in Modena and cancelled his first planned public reappearance a few months later.
Pavarotti is known for helping to bring opera to the masses and performed to stadium audiences around the world.
A TV station in his home city said he was unconscious and suffering from kidney failure. Family and friends had gathered at his villa to be near him.
Career chart
Pavarotti became popular after a stand-in appearance at London's Covent Garden in 1963.
He later teamed up with Spanish tenors Placido Domingo and Jose Carreras at the 1990 World Cup and introduced opera classics to an estimated 800 million television viewers.
Sales of opera albums shot up after the gala concert in Rome's Baths of Caracalla and since then Puccini's aria Nessun Dorma from his opera Turandot has been heavily associated with Pavarotti and football.
Like most Italian boys, Pavarotti used to dream of being a football player.
Earlier in his life, Pavarotti's parents wanted him to have a steady job and for a while he worked as an insurance salesman and teacher.
But he started singing on the operatic circuit and his big break came thanks to another Italian opera great, Giuseppe di Stefano, who dropped out of a London performance of La Boheme in 1963.
Covent Garden had lined up "this large young man" as a possible stand-in.
In 1972 he famously hit nine high C notes in a row in Daughter of the Regiment at New York's Metropolitan Opera, which he referred to as "my home".
Thirty years later, Pavarotti was still one of the highest paid classical singers even though his public performances were less frequent.
Medical problems beset the singer in the final years of his career, forcing him to cancel several dates of his worldwide farewell tour.